To the public, Nijuu Mensou is known for his flawlessly executed heists and the advance warnings he sends his victims. But the gentleman thief is no common criminal—he firmly opposes killing and primarily targets those he views as pigs.

One job brings Nijuu Mensou to the Mikamo residence, where 11-year-old Chizuko, nicknamed "Chiko," lives with her aunt Yoshie and uncle Shouji following the death of her parents. While Chiko is the sole inheritor of a substantial fortune, there is more to her family circumstances than meets the eye, and she would like nothing but to escape her home life. Fortunately, her wish comes true when Nijuu Mensou makes off not only with the Mikamos' heirloom gemstone but also with Chiko herself.

Quick to join the infamous thief's crew, Chiko learns the tools of the trade and grows closer to her new partners in crime, attaining the loving family she has always desired. At the same time, she begins to gain notoriety as the daughter of Nijuu Mensou—a title that carries more than its fair share of trouble.